Various types of instruments with display screens, such as sonar devices for pleasure boats and other small marine craft, are designed with threaded holes in the opposed sides of the instrument body. The instrument is typically sold with a gimbal type bracket having openings, which are generally slots, which align with the threaded holes in the instrument body. A pair of handles with threaded rod projections pass through the openings in the bracket and threadedly engage within the threaded holes in the instrument body to suspend the instrument within the bracket. This mounting system allows the instrument to be pivoted to any desired angle for viewing. By tightening the handles so that the bracket is tightly sandwiched between the handle and the instrument body, the instrument may be fixed at a particular angle with respect to the bracket.
By reversing these mounting steps, the instrument may be removed from the instrument bracket. A disadvantage of this removable mounting system is that an instrument is vulnerable to theft.
Locking devices incorporating screw-type locks are well known in the art. Screw-type locks essentially comprise a tumbler housing rotatable in a casing when the proper key is inserted into the housing. The housing has a threaded stud projecting from the non-keyed end of the tumbler housing. The tumbler housing is mounted within the casing so that it rotates within the casing when the key is inserted into the tumbler housing and is held in a fixed position with respect to the casing when the key is withdrawn.
Screw-type locks are of two general types: locks where the threaded stud engages with a threaded opening in a second piece of the lock, such as the locks disclosed in U.S. Pat. No. 4,428,211 to Hermann and U.S. Pat. No. 4,711,106 to Johnson, and locks where the threaded stud engages with a threaded opening in the object to be locked. An example of a locking assembly which utilizes a threaded opening in the object to be locked is U.S. Pat. No. 3,600,912 to Foreman, which discloses a lock assembly for locking sliding shutters.